1. Field of the Invention
This invention relates to a burr hole localizer device for attachment to the head of a patient in order to facilitate localization of an optimum site for posterior burr hole placement, and methods of making such a device. This invention also relates to methods of locating an optimal site for a posterior burr hole prior to a parieto-occipital shunt operation.
2. Background of the Related Art
Ventriculoperitoneal (VP) shunt placement for hydrocephalus is one of the most common procedures in neurological surgery. Hydrocephalus may result from subarachnoid hemorrhage, trauma, tumors, and the like. The technique entails introducing a catheter through brain tissue into one of the lateral ventricles of the brain. Cerebrospinal fluid in the ventricle may be vented through the catheter to relieve signs, symptoms, and sequelae of hydrocephalus.
The current surgical technique for placement of VP shunts was developed in the 1950's by Scarff and has persisted with few modifications. Despite the relative simplicity of this procedure, the complication rate can be significant and includes operative morbidity as well as post-operative infections and obstructions, etc. Surgical technique plays a major role in reducing complications associated with VP shunts. Improper placement of the ventricular catheter may result in neurologic injury from the misplaced catheter or may cause an early proximal shunt obstruction, which is often secondary to blockage by adherent choroid plexus and other debris. The incidence of misplaced catheters is variable and dependent on a variety of factors, including the experience of the surgeon, the size of the targeted ventricle, the surgical approach, and the use of intraoperative guidance, such as fluoroscopy, ultrasound, or endoscopy. Thus, to optimize shunt function and minimize morbidity, proper placement of the proximal catheter is essential.
Two surgical approaches may be used for VP shunt placement, frontal and parietooccipital. Although little data is available, a retrospective series by Albright, et al., J. Neurosurg. 69:883-886 (1988), found good catheter placement in only 55% of frontal shunts and 33% of parieto-occipital shunts. Four cases of ophthalmic injury following ventricular catheter insertion were recently reported, and intracerebral hemorrhages secondary to misplacement have appeared in isolated clinical reports. The rate of such complications is not known. Recently, endoscopic placement of ventricular catheters has been reported with an accurate placement rate of 90%. Neuroendoscopy: Volume 1, Mary Ann Liebert, New York, pp. 29-40 (1992). The disadvantages of this technique are related to the cost of the instrumentation, the added operative time, and the time required for the surgeon to become familiar with the technique. If, however, an accurate, rapid, and inexpensive tool were available to aid in catheter placement, it would simplify the procedure.
A frontal catheter guide fulfilling these criteria has been successfully developed by Ghajar for placement of frontal ventricular catheters. Ghajar, J. B. G., A guide for ventricular catheter placement: technical note. J. Neurosurgery, 63:985-986, 1985. This instrument capitalized on the anatomical observation that a line passing perpendicular to the skull at the coronal suture will intersect the lateral ventricle.
However, parieto-occipital catheter placement has significant advantages over frontal catheter placement. The catheter path necessary for the frontal approach to the ventricles traverses frontal lobe regions having a low seizure threshold. Mechanical irritation of the neural tissue surrounding the catheter may give rise to epileptogenic foci independent of the underlying cause of hydrocephalus. This complicates patient management and increases health care costs, as well as markedly impacting the patient's quality of life.
The anatomy of the head and neck also causes technical difficulties for the surgeon. The distal end of the shunt is subcutaneously tunneled to the peritoneal cavity for implantation. Implantation in the open peritoneum provides an outlet for excess fluid drainage from the ventricles. The catheter path to the abdomen is circuitous from the frontal burr hole, however. The tube must pass posterior to the ear, and generally requires an additional skin incision. These difficulties increase operative time, cost, and complications.
In view of the above considerations, posterior shunt operations are often preferred over frontal shunt procedures (see, for example, J. L. Leggate, et al., J. Neurosurg., 68: 318-319 (1988)). In performing a posterior shunt operation according to the prior art, a catheter is passed from a posterior burr hole towards a frontal or anterior target point on the patient's forehead. Evidently, selection of an appropriate burr hole site is crucial to correct placement of a catheter within the target region (anterior horn of lateral ventricle) of the patient's brain. Notwithstanding, prior to the instant invention, there have been no mechanical or other forms of devices available to aid in the appropriate localization or selection of a posterior burr hole site. Indeed, the current standard practice is to palpate landmarks such as the external occipital protuberance, and to visualize where the burr hole should be located. This procedure is inherently inaccurate, and may result in severe neurologic injury when a catheter passed through a misplaced burr hole inadvertently traverses a critical brain structure (internal capsule).
Other than burr hole site selection, a second source of error in catheter placement during a posterior shunt procedure is insertion of the catheter along an incorrect trajectory. A simple mechanical device, known as the Caroline Guide, which eliminates this second source of error is taught by Howard III, et al. in U.S. Pat. No. 5,569,267, the contents of which are incorporated herein in their entirety.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.